Ferromagnetism in certain alloys with a crystalline B2-structure, such as Fe60Al40, can be switched on, and tuned, via antisite disordering of the atomic arrangement. This disorderinduced B2→A2 phase transition is accompanied by a ∼1% increase in the lattice parameter. The induced ferromagnetism can be switched off as well via atomic rearrangements causing the A2→B2 transition. In this thesis, the B2↔A2 phase transition will be manipulated by ion- as well as laser-irradiation. Ion-irradiation allows for a sensitive control of the degree of antisite disorder and thus can be applied to understand the correlation between gradual disorder and magnetic properties in the Fe60Al40 alloy. The reversibility of the laser-driven B2↔A2 transition will be shown in this work. B2-Fe60Al40 thin films have been disordered systematically by ion-irradiation and correlations between the chemical disorder (1-S), lattice parameter (a0), and the induced saturation magnetization (Ms) have been obtained. As the lattice is gradually disordered,a critical point occurs at 1-S=0.6 and a0=2.91Å, where a sharp increase of the Ms is observed. The regimes below and above the critical regime are characterized by a different, but nearly stable Ms behaving paramagnetic and ferromagnetic, respectively. Density functional theory (DFT) calculations suggest that below the critical point the system magnetically behaves as it would still be fully ordered, i.e. paramagnetic, whereas above, it is largely the increase of a0 in the disordered state that determines the Ms. Furthermore, disordered thin films possessing various open-volume defect types have been ordered via thermal annealing. The A2→B2 ordering process occurs by the vacancy diffusion mechanism and the ordering rate shows a strong dependence on the defect types, as obtained from ab-initio DFT calculations: The ordering rate is increased by mono-vacancies and decreased by triple defects and vacancy clusters. The defects can be engineered by a thermal pre-annealing and/or ion-irradiation offering a control of the subsequent ordering process. Additionally, the reversible disordering and subsequent reordering implying an on and off switching of ferromagnetism, respectively, is demonstrated by applying femtosecond laser pulse irradiation. The irradiation with a single laser pulse above the threshold fluence induces chemical disorder and hence ferromagnetism. A subsequent laser-irradiation below the threshold ŕuence causes a reordering at the surface erasing the ferromagnetism. The laser-irradiation leads to a melting and subsequent solidification of the material; if the solidification temperature is lower than the melting temperature, the liquid is supercooled. Simulations reveal the crucial role of the extent of supercooling: A single laser pulse above the threshold fluence causes a strong undercooling of the liquid phase before solidification limiting the vacancy diffusion and hence ordering. Laser pulsing below the threshold forms a limited supercooled surface region that solidifies at sufficiently high temperatures, enabling vacancy diffusion-assisted reordering.:1 Introduction and Fundamentals 1.1 Magnetism and Structure in Chemically Ordered Materials 1.1.1 Effects Induced by Chemical Disorder 1.1.2 Properties of Fe-Al Alloys 1.2 Modiőcation of B2 Materials 1.2.1 Interaction of Ions with Solids 1.2.2 Laser-Solid Interaction 1.3 Motivation 2 Experimental and Theoretical Methods 2.1 Sample Preparation 2.1.1 Magnetron Sputtering 2.1.2 Annealing Process 2.1.3 Ion-Irradiation 2.1.4 Laser-Irradiation 2.2 Structural Characterization 2.2.1 X-Ray Diffraction 2.2.2 Rutherford Backscattering Spectrometry 2.2.3 Transmission Electron Microscopy 2.3 Magnetic Characterization 2.3.1 Vibrating Sample Magnetometry 2.3.2 Spin-Resolved Photoemission Electron Microscopy 2.4 Defect Analysis by Positron Annihilation Spectroscopy 2.5 Theoretical Approaches 2.5.1 DFT Calculations on the Properties of Fe60Al40 2.5.2 Ab-initio Calculations of Positron Lifetimes in Fe60Al40 2.5.3 Simulations on the Laser-Irradiation of Fe60Al40 3 Unraveling Magneto-Structural Correlations 3.1 Characterization of Ordered B2 and Disordered A2 Films 3.1.1 Experiments 3.1.2 Structural Properties 3.1.3 Magnetic Properties 3.1.4 Summarizing Remarks 3.2 Systematic Disordering by Ion-Irradiation 3.2.1 Experiments 3.2.2 Structural Characterization 3.2.3 Analysis of Magnetic Properties 3.2.4 Correlation of Structural and Magnetic Properties 3.2.5 Comparison to Previously Reported Data 3.2.6 Theoretical Calculations 3.2.7 Discussion and Summarizing Remarks 4 Defect-Mediated Atomic Rearrangements 4.1 Experiments 4.2 Analysis of Magnetic Properties 4.3 Defect Characterization 4.4 Ab-initio Calculations of Positron Lifetimes 4.5 Discussion 5 Laser Pulse Induced Reversible Order-Disorder Transition 5.1 Experiments 5.2 Results 5.3 Simulations 5.4 Discussion 6 Conclusions / In bestimmten Legierungen mit einer kristallinen B2-Struktur, wie beispielsweise Fe60Al40, kann durch eine chemische Unordnung Ferromagnetismus erzeugt und modifiziert werden. Dieser durch Unordnung hervorgerufene B2→A2 Phasenübergang geht mit einer Vergrößerung des Gitterparameters von ungefähr 1% einher. Der erzeugte Ferromagnetismus kann durch eine atomare Neuordnung, d.h. durch den A2→B2 Phasenübergang, wieder abgeschaltet werden. In der vorliegenden Arbeit wird der B2↔A2 Phasenübergang mittels Ionen- und Laserbestrahlung hervorgerufen und kontrolliert. Ionenbestrahlung ermöglicht eine präzise Kontrolle des Unordnungsgrades und kann daher eingesetzt werden, um den Zusammenhang zwischen gradueller Unordnung und magnetischen Eigenschaften in der Fe60Al40 Legierung zu untersuchen. Die Reversibilität des laserinduzierten B2↔A2 Phasenübergangs wird in der vorliegenden Arbeit gezeigt. In B2-Fe60Al40 Dünnschichten ist mittels Ionenbestrahlung systematisch Unordnung erzeugt worden, wodurch die Zusammenhänge von atomarer Unordnung (1-S), dem Gitterparameter (a0) und der erzeugten Magnetisierung (Ms) offengelegt worden. Während der schrittweisen Unordnung des Kristallgitters tritt ein kritischer Punkt bei 1-S=0.6 und a0=2.91Å auf, an welchem Ms stark ansteigt. Die Bereiche unter- und oberhalb des kritischen Bereiches sind durch ein unterschiedliches, aber nahezu gleichbleibendes Ms charakterisiert. Das Verhalten ist para- bzw. ferromagnetisch. Berechnungen mittels Dichtefunktionaltheorie (DFT) deuten an, dass sich das System unterhalb des kritischen Punktes verhält, als wäre es noch vollständig geordnet, d.h. paramagnetisch; wohingegen Ms oberhalb des kritischen Bereiches größtenteils durch den Anstieg des Gitterparameters bestimmt wird. Darüber hinaus sind ungeordnete Dünnschichten mit verschiedenen Typen leerstellenartiger Defekte mittels Wärmebehandlung neu geordnet worden. Der A2→B2 Ordnungsprozess geschieht auf der Basis des Leerstellendiffusionsmechanismus. Die starke Abhängigkeit der Ordnungsrate von den Defekttypen ist mittels ab-initio DFT Berechnungen bestätigt worden: Die Ordnungsrate wird durch Einzel-Leerstellen erhöht und sinkt durch Dreifach-Defekte und Leerstellencluster. Die Defekte können durch eine vorherige Wärmebehandlung und/oder Ionenbestrahlung manipuliert werden, wodurch der darauffolgende Ordnungsprozess kontrolliert werden kann. Des Weiteren wird die reversible Unordnung und anschließende Neuordnung, d.h. ein Erzeugen bzw. Abschalten von Ferromagnetismus, durch die Bestrahlung mit Femtosekunden- Laserpulsen demonstriert. Die Bestrahlung mit einem einzelnen Laserpuls mit einer Fluenz über dem Schwellenwert erzeugt atomare Unordnung und damit Ferromagnetismus. Eine anschließende Laserbestrahlung unterhalb der Schwellenŕuenz bewirkt eine Neuanordnung der Atome an der Oberfläche und damit einem Auslöschen des Ferromagnetismus. Die Laserbestrahlung führt zu einem Aufschmelzen und dem anschließenden Erstarren des Materials; liegt die Erstarrungstemperatur unterhalb der Schmelztemperatur, so ist die Schmelze unterkühlt. Die ausschlaggebende Rolle des Grades der Unterkühlung wird durch Simulationen aufgezeigt: Ein einzelner Laserpuls über der Schwellenfluenz führt zu einer starken Unterkühlung der flüssigen Phase vor der Erstarrung, wodurch die Leerstellendiffusion und damit die atomare Neuordnung eingeschränkt werden. Durch Laserpulse unterhalb der Schwellenfluenz wird der Oberŕächenbereich kaum unterkühlt und erstarrt anschließend bei hinreichend hohen Temperaturen, um eine leerstellendiffusionsunterstützte Neuanordnung der Atome zu ermöglichen.:1 Introduction and Fundamentals 1.1 Magnetism and Structure in Chemically Ordered Materials 1.1.1 Effects Induced by Chemical Disorder 1.1.2 Properties of Fe-Al Alloys 1.2 Modiőcation of B2 Materials 1.2.1 Interaction of Ions with Solids 1.2.2 Laser-Solid Interaction 1.3 Motivation 2 Experimental and Theoretical Methods 2.1 Sample Preparation 2.1.1 Magnetron Sputtering 2.1.2 Annealing Process 2.1.3 Ion-Irradiation 2.1.4 Laser-Irradiation 2.2 Structural Characterization 2.2.1 X-Ray Diffraction 2.2.2 Rutherford Backscattering Spectrometry 2.2.3 Transmission Electron Microscopy 2.3 Magnetic Characterization 2.3.1 Vibrating Sample Magnetometry 2.3.2 Spin-Resolved Photoemission Electron Microscopy 2.4 Defect Analysis by Positron Annihilation Spectroscopy 2.5 Theoretical Approaches 2.5.1 DFT Calculations on the Properties of Fe60Al40 2.5.2 Ab-initio Calculations of Positron Lifetimes in Fe60Al40 2.5.3 Simulations on the Laser-Irradiation of Fe60Al40 3 Unraveling Magneto-Structural Correlations 3.1 Characterization of Ordered B2 and Disordered A2 Films 3.1.1 Experiments 3.1.2 Structural Properties 3.1.3 Magnetic Properties 3.1.4 Summarizing Remarks 3.2 Systematic Disordering by Ion-Irradiation 3.2.1 Experiments 3.2.2 Structural Characterization 3.2.3 Analysis of Magnetic Properties 3.2.4 Correlation of Structural and Magnetic Properties 3.2.5 Comparison to Previously Reported Data 3.2.6 Theoretical Calculations 3.2.7 Discussion and Summarizing Remarks 4 Defect-Mediated Atomic Rearrangements 4.1 Experiments 4.2 Analysis of Magnetic Properties 4.3 Defect Characterization 4.4 Ab-initio Calculations of Positron Lifetimes 4.5 Discussion 5 Laser Pulse Induced Reversible Order-Disorder Transition 5.1 Experiments 5.2 Results 5.3 Simulations 5.4 Discussion 6 Conclusions

Two different aluminium alloys, AA6111 (Al-Mg-Si) and AA7055 (Al-Mg-Zn), were chosen as the aluminium alloys to be welded with DC04, and two welding methods (USW and FSSW) were selected to prepare the welds. Selected pre-welded joints were then annealed at T=400 - 570oC for different times. Kinetics growth data was collected from the microstructure results, and the growth behaviour of the IMC layer was found to fit the parabolic growth law. A grain growth model was built to predict the grain size as a function of annealing time. A double-IMC phase diffusion model was applied, together with grain growth model, to predict the thickness of each phase as a function of annealing time in the diffusion process during heat treatment. In both material combinations and with both welding processes a similar sequence of IMC phase formation was observed during the solid state welding. η-Fe2Al5 was found to be the first IMC phase to nucleate. The IMC islands then spread to form a continuous layer in both material combinations. With longer welding times a second IMC phase, θ-FeAl3, was seen to develop on the aluminium side of the joints. Higher fracture energy was received in the DC04-AA6111 joints than in the DC04-AA7055 joints. Two reasons were claimed according to the microstructure in the two joints. The thicker IMC layers were observed in the DC04-AA7055 joints either before or after heat treatment, due to the faster growth rate of the θ phase. In addition, pores were left in the aluminium side near the interface as a result of the low melting point of AA7055.The modelling results for both the diffusion model and grain growth model fitted very well with the data from the static heat treatment. Grain growth occurred in both phases in the heat treatment significantly, and was found to affect the calculated activation energy by the grain boundary diffusion. At lower temperatures in the phases with a smaller grain size, the grain boundary diffusion had a more significant influence on the growth rate of the IMC phases. The activation energies for the grain boundary diffusion and lattice diffusion were calculated as 240 kJ/mol and 120 kJ/mol for the η phase, and 220 kJ/mol and 110 kJ/mol for the θ phase, respectively. The model was invalid for the growth of the discontinuous IMC layers in USW process. The diffusion model only worked for 1-Dimensional growth of a continuous layer, which was the growth behaviour of the IMC layer during heat treatment. However, due to the highly transient conditions in USW process, the IMC phases were not continuous and uniform even after a welding time of 2 seconds. Therefore, the growth of the island shaped IMC particles in USW was difficult to be predicted, unless the nucleation stage was taken into consideration.

This thesis presents the formation mechanism of intermetallics formed at Fe-Al film interfaces. Al thin films with different initial film thicknesses were coated on low carbon steel substrates by physical vapor deposition (PVD). By annealing the system at different temperatures and for different time intervals, several intermetallic phases were observed. X-Ray, SEM and EDS studies showed that intermetallic phases FeAl2 and Fe2Al5 are most dominant phases which were observed and they formed sequentially on the contrary of intermetallics which formed synchronous in bulk materials.

The Thin Slab Cast Direct Rolling (TSCDR) process offers several economic and environmental advantages. The elimination of slab reheating and roughing deformation, however, leave fewer opportunities for grain refinement and some large grains persist in the microstructure. To solve this problem, a new chemistry which leads to a two-phase mixture of ferrite and austenite over a wide temperature range was introduced by Zhou et al. The two phase mixture is highly resistant to grain coarsening leading to a small initial grain size compared with the grain size of conventional TSCDR slab. In addition, ferrite and austenite co-exist over wide range of temperature in many third generation steels, making it extremely important to understand the hot deformation behavior of these materials, which have traditionally received less attention in the literature. In order to investigate the microstructure evolution of ferrite-austenite mixtures during thermomechanical processing, an Al containing model alloy, for which the two phases co-exist over a wide temperature range, was designed. Two types of experiments were carried out: the first involved single hit hot compression tests; and the second involved stress relaxation tests. According to the microstructure observation the main change of austenite microstructure under deformation conditions was a decrease in the spacing of the austenite particles within the ferrite matrix. In other words the austenite phase behaved as hard particles inside a soft ferrite matrix. Hot deformation led to the static recrystallization of the ferrite matrix. The most favourable nucleation sites were in the vicinity of the old grain boundaries and the around austenite particles. The recovery and recrystallization kinetics of ferrite were analyzed using the stress relaxation test. Based on analysis of the stress relaxation tests, more than 95% of stored energy was consumed by recovery, while static recrystallization consumed less than 5% of the stored energy. The retardation of recrystallization in the model alloy is attributed to both the high rate of recovery in BCC materials and texture effects. / Thesis / Master of Applied Science (MASc) / The Thin Slab Cast Direct Rolling (TSCDR) process offers several economic and environmental advantages. The elimination of slab reheating and roughing deformation, however, leave fewer opportunities for grain refinement and some large grains persist in the microstructure. To solve this problem, a new chemistry which leads to a two-phase mixture of ferrite and austenite over a wide temperature range was introduced by Zhou et al. The two phase mixture is highly resistant to grain coarsening leading to a small initial grain size compared with the grain size of conventional TSCDR slab. In addition, ferrite and austenite co-exist over wide range of temperature in many third generation steels, making it extremely important to understand the hot deformation behavior of these materials, which have traditionally received less attention in the literature. In order to investigate the microstructure evolution of ferrite-austenite mixtures during thermomechanical processing, an Al containing model alloy, for which the two phases co-exist over a wide temperature range, was designed. Two types of experiments were carried out: the first involved single hit hot compression tests; and the second involved stress relaxation tests. According to the microstructure observation the main change of austenite microstructure under deformation conditions was a decrease in the spacing of the austenite particles within the ferrite matrix. In other words the austenite phase behaved as hard particles inside a soft ferrite matrix. Hot deformation led to the static recrystallization of the ferrite matrix. The most favourable nucleation sites were in the vicinity of the old grain boundaries and the around austenite particles. The recovery and recrystallization kinetics of ferrite were analyzed using the stress relaxation test. Based on analysis of the stress relaxation tests, more than 95% of stored energy was consumed by recovery, while static recrystallization consumed less than 5% of the stored energy. The retardation of recrystallization in the model alloy is attributed to both the high rate of recovery in BCC materials and texture effects.

<p> Aluminum is usually added to the zinc bath to form an Fe-Al interfacial layer which retards the formation of a series of Fe-Zn intermetallic compounds during the hot-dip galvanizing process. However, experimentally exploring the inhibition layer formation and obtaining useful experimental data to understand the mechanisms is quite challenging due to short times involved in this process. In this study, a galvanizing simulator was used to perform dipping times as short as O.ls and rapid spot cooling techniques have been applied to stop the reaction between the molten zinc coating and steel substrate as quickly as possible. In addition, the actual reaction time has been precisely calculated through the logged sample time and temperature during the hot-dipping process. The kinetics and formation mechanism of the inhibition layer was characterized using SEM, ICP and EBSD based on the total reaction time. For bath containing 0.2wt% dissolved AI, the results show that FeA13 nucleates and grows during the initial stage of the inhibition layer formation and then Fe2Als forms by a diffusive transformation. The evolution of the interfacial layer formed in a zinc bath with 0.13wt% dissolved AI, including Fe-Aland Fe-Zn intermetallic compounds, was a result of competing reactions. In the initial period, the Fe-Al reaction dominated due to high thermodynamic driving forces. After the zinc concentration reached a critical composition in the substrate grain boundaries, formation of Fe-Zn intermetallic compounds was kinetically favoured. Fe-Zn intermetallic compounds formed due to zinc diffusing to the substrate via short circuit paths and continuously grew by consuming Fe-Al interfacial layer after samples exited the zinc bath due to the limited Al supply. A mathematical model to describe the formation kinetics as a function of temperature for the 0.2wt% Al zinc bath was proposed. It indicated that the development of microstructure of the interfacial layer had significant influence on the effective diffusion coefficient and growth of this layer. However, the model underestimates the AI uptake by the interfacial layer, particularly at higher temperatures. This is thought to be due to the effect of the larger number of triple junctions in the inhibition layer leading to an underestimation of the effective diffusivity. </p> / Thesis / Master of Science (MSc)

Aluminium is usually added to the continuous hot-dip galvanizing bath to improve coating ductility and adhesion through the rapid formation of a thin Fe-Al intermetallic layer at the substrate-liquid interface, thereby inhibiting the formation of brittle Fe-Zn intermetallic compounds. On the other hand, Mn is essential for obtaining the desired microstructure and mechanical properties in advanced high strength steels, but is selectively oxidized in conventional continuous galvanizing line annealing atmospheres. This can deteriorate reactive wetting by the liquid Zn(Al,Fe) alloy during galvanizing and prevent the formation of a well developed Fe-Al interfacial layer at the coating/substrate interface, resulting in poor zinc coating adherence and formability. However, despite Mn selective oxidation and the presence of surface MnO, complete reactive wetting and a well developed Fe-Al interfacial layer have been observed for Mn-containing steels. These observations have been attributed to the aluminothermic reduction of surface MnO in the galvanizing bath. According to this reaction, MnO is reduced by the bath dissolved Al, so the bath can have contact with the substrate and form the desired interfacial layer. Heat treatments compatible with continuous hot-dip galvanizing were performed on four different Mn-containing steels whose compositions contained 0.2-3.0 wt% Mn. It was determined that substrate Mn selectively oxidized to MnO for all alloys and process atmospheres. Little Mn surface segregation was observed for the 0.2Mn steel, as would be expected because of its relatively low Mn content, whereas the 1.4Mn through 3.0Mn steels showed considerable Mn-oxide surface enrichment. In addition, the proportion of the substrate surface covered with MnO and its thickness increased with increasing steel Mn content.A galvanizing simulator equipped with a He jet spot cooler was used to arrest the reaction between the substrate and liquid zinc coating to obtain well-characterized reaction times characteristic of the timescales encountered while the strip is resident in the industrial continuous galvanizing bath and short times after in which the Zn-alloy layer continues to be liquid (i.e. before coating solidification). Two different bath dissolved Al contents (0.20 and 0.30 wt%) were chosen for this study. The 0.20 wt% Al bath was chosen as it is widely used in industrial continuous galvanizing lines. The 0.30 wt% Al bath was chosen to (partially) compensate for any dissolved Al consumption arising from MnO reduction in the galvanizing bath.The Al uptake increased with increasing reaction time following non-parabolic growth kinetics for all experimental steels and dissolved Al baths. For the 0.20 wt% dissolved Al bath, the interfacial layer on the 1.4Mn steel showed the highest Al uptake, with the 0.2Mn, 2.5Mn and 3.0Mn substrates showing significantly lower Al uptake. However, increasing the dissolved bath Al to 0.30 wt% Al resulted in a significantly increased Al uptake being observed for the 2.5Mn and 3.0Mn steels for all reaction times. These observations were explained by the combined effects of the open microstructures associated with the multi-phase nature of an oxide-containing interfacial layer and additional Al consumption through MnO reduction. For instance, in the case of the 1.4Mn steel, the more open interfacial layer structure accelerated Fe diffusion through the interfacial layer and increased Al uptake versus the 0.2Mn substrate for the same bath Al. However, in the case of the 2.5Mn and 3.0Mn substrates and 0.20 wt% Al bath, additional Al consumption through MnO reduction caused the interfacial layer growth to become Al limited, whereas the very open structure dominated growth in the case of the 0.30 wt% Al bath and resulted in the changing the growth kinetics from mixed diffusion-controlled to a more interface controlled growth mode. A kinetic model based on oxide film growth (Smeltzer et al. 1961, Perrow et al. 1968) was developed to describe the Fe-Al interfacial layer growth kinetics within the context of the microstructural evolution of the Fe-Al interfacial layer for Mn-containing steels reacted in 0.20 wt% and 0.30 wt% dissolved Al baths. It indicated that the interfacial layer microstructure development and the presence of MnO at the interfacial layer had significant influence on the effective diffusion coefficient and interfacial layer growth rate. However, in the cases of the 2.5Mn and 3.0Mn steels in 0.20 wt% Al bath, the kinetic model could not predict the interfacial layer Al uptake, since the Fe-Al growth was Al limited. In fact, in these cases, additional Al was consumed for reducing their thicker surface MnO layer, resulted in limiting the dissolved Al available for Fe-Al growth. / Dissertation / Doctor of Science (PhD)

No description available.

La fusion sélective par laser (Selective Laser Melting, SLM), une des techniques de la fabrication additive (AM), permet la production de pièces en trois dimensions (3D) de formes complexes directement à partir de poudres métalliques. Elle présente de nombreux avantages significatifs par rapport aux méthodes traditionnelles de fabrication mais se heurte encore à une faible disponibilité des matériaux en poudre.Le travail effectué dans cette étude a donc consisté à étudier et à développer un nouveau moyen pour réaliser in situ des pièces en alliages et en composites à partir de mélanges de poudres.Au niveau expérimental le choix s’est porté sur le système Fer-Aluminium et sur un renforcement par des particules de SiC.Les essais ont permis de constater que dans le processus de fabrication de pièces par SLM la puissance du laser et la vitesse de balayage déterminent au premier chef la densité, la microstructure, la composition de phase et les propriétés mécaniques.À partir d’un mélange de poudres, des phases intermétalliques ont été obtenues en contrôlant les paramètres SLM. Un traitement thermique ultérieur influence les paramètres cristallins, le degré d’ordre et les propriétés mécaniques des pièces ainsi formées.Avec l’utilisation de poudres préalliées, un phénomène de texture a été observé prenant la forme de grains allongés/colonnaires orientés dans la direction de construction.Le renforcement de la matrice de fer par des particules de SiC de différentes tailles conduit à une modification structurale avec la formation de produits d’interaction, perlitie et martensite, conduisant à une amélioration de la résistance à la traction par rapport au Fe pur. / Selective laser melting (SLM), as one of the additive manufacturing (AM) technologies, enables the production of three dimensional (3D) complex parts directly from metal powders. It offers many significant advantages compared with traditional manufacturing methods; however it faces a limited availability of powder materials.The work done during this study consisted in investigating and developing a new way of in situ producing alloys and composites from powder mixtures.The iron-aluminum system and reinforcement by SiC particles were considered.Experiments have shown that the laser power and scanning speed primarily determine the density, microstructure, phase composition and mechanical properties in the manufacturing process of SLM parts.Using pre-alloyed powders, a phenomenon of texture was observed in the form of elongated/columnar grains oriented in the building direction.Using powder mixtures, intermetallic phases were obtained by controlling the SLM parameters. A heat treatment influences the crystal parameters, the degree of order and the mechanical properties of the formed parts.The reinforcement of the iron matrix by SiC particles of several sizes leads to a structural change with the formation of interaction products, perlite and martensite, leading to an improvement in tensile strength compared to pure Fe.

The aim of this work was to improve the heat capacity estimation of a material for usage within a CALPHAD-type assessment. An algorithm is derived that estimates the trend of heat capacity with temperature based on zero Kelvin properties and the thermal expansion coefficient at the Debye temperature. The algorithm predicts not only the trend of heat capacity but also the temperature trend of the volume and the bulk modulus, which can be also included in new thermodynamic databases. The algorithm is used to assess thermophysical properties of the intermetallic phases eta (Fe2Al5), epsilon~(Fe5Al8) and tau4 (FeAl3Si2). The heat capacity of the intermetallic phases zeta, eta, theta and epsilon of the Al-Fe system and of tau4 of the Al-Fe-Si system was measured using DSC. For the phases zeta, eta, and theta, a non-linearly increasing heat capacity approaching the melting temperature was observed. In addition, the heat capacity of three bcc-based Al-Fe samples including the B2-->A2 transition were determined. The Al-rich section of the Al-Fe phase diagram was studied using DTA and quenching experiments. The homogeneity ranges of the intermetallic phases were determined using SEM/WDS measurements. Based on own and literature values, a thermodynamic description of the Al-Fe system was assessed including the modelling of A2/B2 ordering and the homogeneity range of all intermetallic phases. In addition, thermodynamic parameters of the Al-Fe-Si, Al-Fe-Mg, and the Fe-Mg-Si system were assessed to obtain a thermodynamic description of the Al-rich side of the Al-Fe-Si-Mg system, which can be used to study phase transitions of typical A356-aluminium alloys.

L'hydrocondensation des oxydes de carbone sur un catalyseur Fe/Al₂O₃ a été étudiée entre 1 et 30 bars de pression et à des températures de réaction comprises entre 200 et 275°C. L'activité et la sélectivité ont été mesurées en fonction du temps de réaction, conjointement à la caractérisation physico-chimique in situ du fer en volume par spectroscopie Mossbauer et mesures magnétiques, et des espèces superficielles par spectroscopie infra-rouge, thermodésorption programmée et thermoréduction programmée. Les résultats obtenus pour la réaction H₂ + CO ont conduit à l'élaboration d'un mécanisme basé sur la dissociation initiale du monoxyde de carbone, et croissance de chaîne par addition successive d'espèces CH_x (x = 1, 2 ou 3). Le fer est rapidement transformé en carbure de fer Fe_(2+x)C (0 < x < 0,4) dont la teneur en carbone augmente en fonction du temps de réaction. Aucun oxyde de fer ne se forme en quantité décelable. Le vieillissement observé du catalyseur est attribué à la carburation du fer et à l'accumulation de carbone peu réactif. L'étude comparative de la réaction H₂ + CO₂ a mis en évidence l'évolution particulière de l'activité en fonction du temps selon un modèle en trois étapes successives (désactivation, réactivation, nouvelle désactivation) qui ont pu être interprétées à l'aide des études physico-chimiques in situ du catalyseur. L'effet de la pression totale des réactifs de 8 à 30 bars sur l'orientation des sélectivités a été établi. Des alcools homologues sont produits préférentiellement aux hydrocarbures dans certaines conditions de la réaction H₂ + CO, et en particulier : le méthanol à 200-225°C et dès 8 bars de pression. Avec la réaction H₂ + CO₂, les produits prépondérants sont le méthane et le méthanol. L'ensemble des résultats obtenus entre 1 et 30 bars a conduit à l'élaboration d'un schéma réactionnel faisant intervenir le monoxyde de carbone sous forme dissociée pour la production d'hydrocarbures, et simultanément sous forme moléculaire pour la production d'alcools. La nature des sites actifs est discutée.